What Is Fosfomycin?
Fosfomycin, an antibacterial drug produced by actinomycetes of the genus Streptomyces and synthesized from phosphoenolpyruvate, stands out as the only one in its class without a common strain among antibacterials. It comes in both drinkable and injectable forms, with a chemical formula of C3H5CaO4P・H2O for the drinkable version and a similar composition for the injectable form, differing by the presence of calcium (Ca) in the former and sodium (Na) in the latter. Marketed under the trade name “fosmisin,” it is effective against a wide range of Gram-positive and Gram-negative bacteria.
Uses of Fosfomycin
Fosfomycin’s broad spectrum of activity makes it a versatile option, particularly as a second-line treatment against multidrug-resistant bacteria. Its effectiveness varies between oral and injectable forms, targeting bacteria such as Staphylococcus spp., Escherichia coli, Serratia spp., Proteus spp., Morganella morganii, Providencia rettigeli, and Pseudomonas aeruginosa, with the oral form also acting against dysentery bacilli, Salmonella, and Campylobacter spp. It is indicated for pyelonephritis and cystitis among other infections, with the oral form being metabolized through the gastrointestinal tract for intestinal infections, and the injectable form used for sepsis and infections of the lungs and uterus.
Properties of Fosfomycin
1. Mechanism of Action
Fosfomycin inhibits the initial stage of cell wall synthesis, a unique mechanism of action compared to beta-lactam antibiotics, which also target cell wall synthesis but at different stages.
2. Drug Resistance
Though reports of resistance to fosfomycin are less common than with other antibiotics, mutations can confer resistance, notably diminishing its efficacy against strains of Pseudomonas aeruginosa and Escherichia coli.
3. Pharmacokinetics
After administration, fosfomycin is distributed and excreted unchanged in urine. Impaired renal function may hinder its elimination, necessitating dosage adjustments based on the severity of renal impairment.
Characteristics of Fosfomycin
Notably effective under anaerobic conditions, fosfomycin’s oral form is particularly suited for treating intestinal infections, contrasting with aminoglycosides, which are less effective in the absence of oxygen.
Other Information About Fosfomycin
1. Contraindications and Prudent Dosage
While no specific contraindications exist for the oral form, the injectable form should not be used by those with a known hypersensitivity to fosfomycin. Special care is required for patients with a familial history of allergic reactions or hepatic impairment due to the risk of adverse reactions, including increased hepatic enzymes.
2. Points of Caution
Both formulations necessitate caution in patients with renal impairment, particularly the elderly. The injectable form, due to its sodium content, also requires careful consideration in patients with conditions that demand sodium intake restrictions.
3. Adverse Effects
Adverse effects, including severe colitis, pancytopenia, agranulocytosis, thrombocytopenia, and convulsions, have been reported for both forms of fosfomycin, though the exact frequency of these events is unknown.